The general goal or this research is to understand the neural mechanisms underlying spatial cognition and to investigate the role of the right hemisphere in this function. For that purpose, rhesus monkeys will be trained to perform tasks commonly used to determine the spatial capacities of adult human subjects and children during development. These tasks include memorizing locations of visual stimuli, categorizing space explicitly (e.g. "high"/"low"), making comparative spatial judgments (e.g. about "higher/lower"), estimating relative distances (with respect to a reference point, or not), and using Cartesian coordinate axes. Each monkey will be trained in all tasks. The activity of single cells during task performance will be recorded in posterior parietal cortex using 16-microelectrode systems. Posterior parietal cortex is known to be intimately involved in spatial operations and, therefore, we expect cell activity to be modulated involved in the aforementioned tasks and to provide valuable Information concerning their neural mechanisms. In addition, we will test the hypothesis that parietal cortex in the right hemisphere is specialized for spatial operations, a hypothesis based on the differential effects of brain damage on spatial abilities of human patients. For that purpose, we will record simultaneously from symmetric posterior parietal sites of the two hemispheres during performance of all the tasks. The data to be obtained will be analyzed using uni- and multivariate statistical methods to determine the control of these tasks by singe cells and neuronal populations, and to delineate the specific contribution of each one of the cortical areas above to this control. By analyzing normal brain mechanisms, we hope to discover some basic principles of organization underlying spatial deficits observed in brain-damaged people.